Pot burners



A. A. STRUIJ K May 14, 1963 PCT BURNERS Filed May 11. 1960 United StatesPatent Ofilice amass? Patented l t lay id, 1963 1 3,tl39,537 P91 BURNERSAntony Albertus Struijk, Beethoyenlaan 9, Hilversum, Netherlands FiledMay 11, 1%9, Ser. No. 28,497 Claims priority, application NetherlandsMay 20, 1959 13 Qlaims. (Cl. 153-91) The invention relates to a potburner with a pot with a bottom and a flame opening formed in an upperwall and lateral air inlet apertures arranged in the side wall of thepot.

Such devices are generally known. Up till now they consist of acylindrical pot with a slightly concave bottom and a radial or generallyradial upper wall, tapering slightly upwards and having a relativelywide central flame opening, below which in the side wall one or morecircles of air inlet apertures are provided. The whole pot is surroundedby an air conducting jacket which is also generally cylindrical andjoins with the side wall of the pot at the upper end by a ring-shapedupper wall and has a ring-shaped lower Wall with a central air inletopening under the bottom of the burner. The pot space may be furthersubdivided into two or more compartments by one or more intermediatebaflle walls with a central opening for increasing the regulation rangeof the burner. The intermediate baffle walls extend inward from the sidewall approximately parallel to the upper wall. The pot is again providedwith one or more circles of air inlet apertures in the side Wall undereach intermediate baflle Wall. With these burners the evaporation of thefuel, which is admitted at the bottom, takes place mainly in the centerof the lower portion of the pot space, therefore under the relativelywide flame opening and/ or the openings in the intermediate bafliewalls. In consequence of the ascending force of the vapour this latterimmediately ascends through these openings, so that the pot space ismainly filled with air and in this air space a gas column is createdwhich rises centrally in a column the width of the flame opening and ofpassages of the intermediate baffle walls if present and comes in touchwith the admitted air only at the circumference. As a consequence adestructive combustion takes place with a yellow flame with considerablesoot formation (allowable limit soot index 8). For ameliorating thecombustion, therefore, with this kind of burner it is also known toadmit an additional amount of combustion air above the flame opening,but this necessitates a rather long flame space which makes theapplication of this kind of burner, for instance for hearths, ditficult,as with this kind of devices the height of the chimney must be withindetermined limits. Besides, the soot deposit in the chimney may beinconvenient and even dangerous as chimney fires and explosions in thechimney-shaft may be caused. Also, they need a rather high chimney-draftso that the air in the air conducting jacket is admitted centrally andhas to flow through several sharp curves before it enters the pot space.

Also pot burners are known with an oblong pot and a slot-shaped flameopening. These pot burners may also be provided with an intermediateresistance wall. With this known construction the pot has a fully flatupper wall with a flanged flame opening, whereas the intermediateresistance wall consists of two parts sloping slightly upwards. Theflame opening of the intermediate wall is approximately of the samewidth as the main flame opening and in mounted condition an airadmitting slot is formed on both sides along the main flame opening foradditional combustion air. The longitudinal walls of the burner pot areprovided with rows of air inlet apertures from the top to near the.bottom. Also with this known burner the circumstances are such, that aband-shaped fuel vapour column is formed, which comes in contact withair only at the outside, so that in this case only a destructivecombustion with yellow flame and soot formation can take place, whereasrelatively high flame space is necessary.

Furthermore a round burner is known, of which the pot is of generallyspherical form with a flattened portion serving as the bottom and arelatively wide flame opening lying opposite thereto. The spherical potis cut through along a meridian plane parallel to the bottom andcontains, about at the level of this meridian plane, a battle ringstructure with a central opening. The partially spherical pot has on theoutside of the. upper part an air conducting jacket merging with a slotunder a ring-shaped upper Wall. The pot wall is, for the rest, providedwith air inlet apertures in both parts. This construction works in thesame manner as the first of the above described known constructionshaving a cylindrical pot and it therefore also gives a destructivecombustion with a yellow flame and requires a rather high flame spaceand a rather strong draft.

The present invention aims at providing a pot burner in which the abovedrawbacks are avoided.

According to the invention this is obtained by making the pot generallyii-shaped in cross-section with the closed under portion forming thebottom, while the upper Wall in cross-section has converging partsbeginning at the broadest part of the burner and running slantinglyupwards and the upper wall parts define the flame opening, while the airinlet apertures are only provided in the widening lower part of theburner and may also be present over the flame opening, the whole burnerbeing constructed and dimensioned in such a manner that during operationthe pot is filled completely or practically completely with fuel vapourand the air flowing in through the air inlet apertures gives a stablehydroxylative combustion on the whole regulation range by this shapingof the pot, which in the round construction is mainly double conical, apot space is obtained which is filled completely with fuel vapour whenthe passage through the flame opening in the upper part and in theintermediate baflle wall respectively and the direction of the incomingair are well calculated, and the fuel vapour will burn underhydroxylation by the incoming air. This hydroxylative combustion givesblue sootless flame, so that a combustion is obtained having a sootindex 0 and requires practically no flame space. With the constructionas a round burner, however, the capacity is limited since with greaterdimensions the admitted air will soon no longer cover the flame opening.Therefore preferably the burner is carried out as an oblong burner witha relatively narrow oblong flame opening in the upper wall.- The burnerfurther according to the invention has a generally trough-shaped lowerportion diverging upwards and a mainly roof-shaped upper wall convergingupwards to the middle plane. In this way a stably blue burning potburner of practically any or every desired capacity can be made, whichcan be easily and favourably adapted to the available space, forinstance in hearths, by arranging the burner with the longitudinaldirection parallel to the front and rear sides of the hearth.

In burners with a sufliciently large capacity for heating purposes andfor industrial purposes the flame opening is appropriately provided withan upstanding wall, in which air inlet apertures are also provided, thedistance between these upstanding walls being such, that the air streamsentering through the apertures in these walls will at least reach to themiddle between these two upstand ing walls and at the utmost just do nottouch the oppoa9 site wall. The air apertures in the diverging lowerportion of the burner pot then serve for a pro-mixing of the fuel vapourduring burning at full capacity, whereas the final combustion takesplace in the flame opening by the air admitted at that place. Inadjustable burners these air inlet apertures in the upstanding wall ofthe flame opening are appropriately closable in order to avoid a toogreat air admittance during working at reduced capacity.

When the pot space is subdivided by one or more intermediate bafflewalls, the intermediate wall or walls extend in a roof-shape from thediverging side walls of the lower portion of the burner and with theunder part belonging to it, they enclose a space which has generally thesame shape as, or is similar to, the whole burner pot but isproportionally smaller and the flame openings be coming larger orbroader at each higher level. This has a result that a burner with avery large regulation range of for instance 1:10 or more can be obtainedwhich besides burns blue on the whole regulation range.

In practice the side walls of the lower part are made appropriately asa. flight of stairs with a number of steps corresponding to the numberof parts into which the burner space is subdivided by the intermediatebaflle walls. In this way, it becomes possible to use at least thelowermost of the horizontal parts of the side walls of the lower portionof the burner pot at the same time for supporting one or moreroof-shaped intermediate baflle Walls. At the same time the possibilityarises to arrange the air inlet apertures in the burner pot in or nearthe re-entering angles of the staircase-shaped side walls, whereby afavourable inflow of the air is obtained with possibly less resistanceand without time consuming bending out of the edges of the air inletapertures. In this case the air inlet apertures are appropriatelydrilled in such a manner through the side walls that they are directedto the mouth of the spaces formed by the roofshaped intermediate bafllewalls or a little under it.

In the upstanding wall of the flame opening the air inlet apertures areappropriately drilled horizontally or slightly sloping upwards. The aircurrents flowing in through them then cover nearly the whole width ofthe flame opening, but are bent up at the end by the vapour streamflowing out in such a manner that they do not hit the opposite wall ofthe flame opening, so that this latter is not unnecessarily locallyheated, whereby cracking of the fuel would be caused and the combustionwould become destructive but, on the other hand, the space under theflame opening is closed by an air curtain and the combustion takes placethereby.

Preferably the air inlet apertures lie in the upstanding walls of theflame opening alternately, whereby the whole flame opening can becovered by the air inlet apertures for a complete combustion without thenecessity of these apertures having to lie particularly near one anotherin each of the walls. The burner, however, can also be made in such amanner, that between the horizontal or generally horizontal air inletapertures arranged opposite one another further air inlet aperturesslanting upwards are provided. It has proved that this measure can beappropriate for meeting hum if present during working at full capacity,or anyway it can be of help for it.

The burner further possesses an air conducting jacket which, accordingto the invention, joins the upper edge of the upstanding walls of theflame opening at the top end and runs from there at first nearlyparallel with the upper wall parts of the burner, sloping to theoutside, preferably somewhat diverging in downwards direction, and then,after a gradual bend, straight or nearly straight downwards, laterallyscreening the under portion of the burner. Such a jacket, in cooperationwith the shape of the burner, gives a very favourable flow of the air tothe air inlet apertures with possibly less resistance, so that theinflowing air loses as little as possible of its velocity and a burneraccording to the invention can easily burn with natural draft. It hasfurther proved that the burner remains stably burning blue with thedraft fluctuations occurring in practice. While no particularly highchimney-shaft or other means for augmenting the draft in thechimney-shaft is necessary, a burner according to the invention can burnwell without difficulties, and can also burn well on upper floors ofhouses, in which case the chimney-shaft is short. A draft however isabsolutely necessary with the blue burner according to the invention;this is contrary to the known blue burners such as the sleeve typevaporizing burners.

In practice the side walls of the upper portion and the roof-shapedintermediate baflle walls or the connecting line of the end edgesthereof for bent intermediate baflle walls, are carried out in such amanner that they make an angle of about -70", preferably of about -50",with the horizontal plane.

The invention will now be described with reference to an embodimentshown in the drawing by way of example. In the drawing:

FIG. 1 shows a cross-section of an oblong pot burner according to theinvention with two intermediate bafile walls and an air conductingjacket,

FIGURE 1A is a fragmentary section similar to FIG- URE 1 showing aslightly different arrangement of air openings, and

FIG. 2 shows a top elevation of a burner according to FIG. 1, in whichthe air conduction jacket is omitted.

In the drawing 1 indicates the troughor guttershaped vaulted bottom ofthe burner pot to which the liquid fuel is admitted in known manner andin which this fuel is brought to vaporisation. This bottom part of theburner pot merges into side walls 2 generally slanting to the outsideand which are partly continued in dotted lines at 2a and merge about inthe middle of the height of the burner in a short vertical portion 3,3a, which thereafter again runs up slantingly at an angle of about 50 at4. At the upper end the upper wall parts 4 form the flame opening 5.Above it they are provided with upstanding walls 6 with a flange 7extending outwards. The dotted lines 2a and 3a in the drawing give, withthe joining lines 2, 3 and 4, the general shape of the burner. Thisburner, therefore, has mainly a double conical or angular bulging oblongshape. In the embodiments the side walls of the under part are howeverstair-step-shaped between the lowermost straight portion 2 and the shortintermediate portion 3 with horizontal portions 8, 9 and 10 and verticalportions 11 and 12. The horizontal portions 8 at the same time serve forsupporting a roof-shaped intermediate baflle wall 13. The roof-shapedintermediate baflle wall parts 13 are at an angle of about 40 and form anarrow passage 14 therebetween. In the re-entering angle between theside wall portions 2 and 8 air inlet apertures or openings 15 areprovided, drilled in at an angle of about 50 to the horizontal, asindicated by the arrows 16. In this case the arrows 16 cross one anothera short distance below the opening 14 in the center of the burner or inthe longitudinal center plane of the oblong burner. As appears from thedrawing, the lowermost pot space, which is closed at the upper side bythe intermediate baflie walls 13, is generally similar to the totalburner space. The lowermost portion of the burner therefore forms astably blue-burning small pot burner with a flame opening 14. On thesecond step 9 of the stair-step-shaped side walls of the burner thererests a second roof-shaped intermediate baflle wall 17 forming a passage18, the width of which is larger than the opening 14, but smaller thanthat of the flame opening 5, and which is carried out as a generallyhalf-circle-shaped dome of which the chord lines 19 between the edges,which are shown in dotted lines in the drawing, are at an angle of about50 with the horizontal plane. A row of air inlet apertures 20' isarranged in the horizontal portion 9 at each side near the junction ofwall 11 with wall 9, the apertures in this case being drilled at anangle of as is shown by the arrows 21, so that they cross one another ata short distance below the opening 18 in the longitudinal central planeof the burner. Also the part of the pot burner under the intermediatebattle wall 17, when the intermediate baffle wall 13 is ignored for amoment, again forms a pot space which is generally similar to the wholeburner space.

In the re-entering angle between the side wall portions and 1'2, a rowof air inlet apertures or openings 22 is arranged on both sides, w hichapertures or openings are also drilled at an angle of 45 as indicated bythe arrows 23 which at the same time indicate the direction of theentering air. These air currents 2.3 meet one another at a shortdistance under the primary flame opening 5 in the longitudinal centralplane of the burner. In the upstanding walls 6 of the flame opening 5,finally, further or additional air admitting apertures or openings 24are drilled, somewhat sloping upwards. These air admitting apertures oropenings can be closed with the aid of valves 25, if desired.

As is shown in FIG. 2, the air inlet apertures 24 are spaced alternatelyin the opposite upstanding walls 6, so that the air streams 24a flowalternately in opposite directions. Between these generally horizontallydirected air inlet apertures, if desired, further air inlet apertures,directed slantingly upwards as seen in FIG. 1A, may be providedalternately and opposite the horizontal apertures or openings, wherebythe quietness of the burner can be favourably influenced. The slantingair inlet apertures may be at an angle which may amount up to Gil-70.

Under the flange 7 of the upstanding walls 6 of the burner mouth the airconducting jacket 26 is connected, which runs down from the flange,slanting outwards, diverging a little with respect to the sloping upperwalls 4 of the burner and merges with a gradual bend 27 at the level ofthe middle portion 3 of the burner in a portion running verticallydownward.

The oblong burner shown has at each end a plane end wall 29, which canat the same time form the end wall of the air conducting jacket. Formounting the intermediate bafile walls 13 and 17 the burner is composedof two parts which are interconnected for instance at 30, but may alsobe connected e.g. above the step 19. The portion lying under theconnecting place 30 is connected in a rigid and liquid-tight manner withthe end walls, for instance by welding, at least with the bottom part 1,2 up to the air inlet apertures 15.

However, with an oblong construction the pot can also be fully connectedrigidly with the end walls 29 and form a unit as the intermediate bafflewalls in this case each consist of two parts, which can be brought ineasily from above through the burner mouth 5. The roof-shapedintermediate walls rest on supports arranged on the end walls 29.However with an adequate construction of the burner it is also possibleto interconnect the two parts of the intermediate walls to arigid unitby narrow connecting strips at the ends and/or at one of moreintermediate places.

As further appears from the drawing, the air inlet encounters verylittle resistance as even the air streams to the air admitting aperturesof the flame opening have to pass through only two gradual bends \ofless than 90, as is indicated by the arrows 31, whereas the air streamsto the remaining burner spaces have to make only a single slight curveand besides the air is forced to the air admitting apertures by thewalls of the steps. The burner therefore has only a very low airresistance, so that it can also work undisturbedly at a relatively lowdraft. The air sucked through the burner by the draft thereforeencounters very little resistance on its way through the burner wherebywith a low draft very strong air streams enter into the burner potthrough the perforations in question so they can be accurately directedto the right places and by the great air velocity cause the eddycurrents in the mixing chambers which are necessary for a good mixing ofair and fuel vapour for obtaining a hydroxylative combustion.

The working of the burner is as follows:

When the burner works at full capacity the valves 25 are in the openposition as indicated in FIG. 1. The fuel vapor-ises on thegutter-shaped bottom 1, 2 and is mixed with the air flowing in throughthe air admitting apertures '15, 2t and 22. The amount of air admittedis insuflicient for obtaining a combustible fuel-air-mixture. Combustionthen only occurs by the admittance of air through the air admittingapertures 24 in the upstanding walls 6 of the burner mouth 5. Thecombustion occurs completely and stably with a blue flame, that is, witha large number of flame tongues around the air flowing in through theapertures. The combustion is completely sootless, while no flame spaceover the burner mouth is necessary. It is possible to arrange a numberof glowing members over the burner mouth, on which no deposit is formed.The draft, which the burner requires, is about one-half of that of anormal pot burner. The flame is, besides, insensitive to fluctuations ofthe draft. When the burner is regulated downwardly, the flame graduallysinks down into the burner, but the burner remains burning with a blueflame. At a definite moment the air admitting apertures 24 are no longernecessary and it is possible to close them by the valves 25 in order toprevent the sucking in of unnecessary The burner then remains burningwith a blue flame with the air admitted through the air admittingapertures 15, 20 and 22. When the burner is further regulated, theopening 18 will serve as flame opening. Thereafter, on furtherregulating, the flame sinks to the secondary flame opening 14 and whenstill further regulated it sinks into the space which is closed by theintermediate baffie walls 13. Thus the burner can be regulated up anddown in a proportion of 1:10 or more, during which a stablehydroxylative combilStiOil, thereforewith a blue flame, continuouslytakes p ace.

The invention is described above with reference to an operative example,but it is not limited to the embodiment shown. For instance the halfcircular intermediate baffle wall 17 can be replaced by a roof-shapedintermediate wall with plane, or less bent plates. Furthermore, underspecial conditions it is possible to alter the slant of the roof-shapedintermediate baflle walls and of the upper wall of the burner pot. Alsothe direction of the air inlet apertures may be changed to some extent.The roof-shaped intermediate baflle walls 13 can also be made more orless vaulted, as well as the sloping upper walls. An essential is, thatthe intermediate walls enclose spaces which are similar or generallysimilar to that of the whole burner and the openings in the intermediatebaflle walls are so dimensioned that these spaces will each, because ofthe air streams directed on the flame openings belonging to it and whichcreate a compression at that place, always provide the conditions for ahydroxylative combustion.

I claim:

1. A pot burner comprising an elongated trough shaped lower portionformed with upwardly diverging walls symmetrically on each side of acenter plane, roof shaped upper portions extending upwardly from theupper edge of each wall of said lower portion and converging upwardly tobound, with said lower portion, a generally diamond shaped enclosure,said upper portions terminating short of the central plane of said lowerportion to form a flame opening, primary air openings solely in thediverging walls of said lower portion, said air openings having means todirect inflowing air upwardly and inwardly from each side of said lowerportion in a plane, the planes of said inflowing air intersecting belowsaid primary flame opening, said converging upper portions terminatingat said primary flame opening in opposed generally parallel upstandingwalls, said upstanding walls being provided with additional air inletopenings to direct 3 air across said primary flame opening in planesnormal to said center plane.

2. The pot burner of claim 1, in which further additional air inletopenings slanting upwards are provided between the generally horizontalair inlet openings arranged opposite one another.

3. The pot burner of claim 1, having an air conducting jacket and inwhich the air conducting jacket at the upper end joins the upper edgesof the upstanding walls of the primary flame opening and the walls ofsaid jacket extend from there first downwardly at each side slantingoutwards approximately parallel with the side walls of the upper portionof the burner and then with a gradual bend extends approximatelystraight downwards screening the under portion of the burner.

4. Apparatus according to claim 1, in which the pot space is subdividedby at least one pair of intermediate resistance walls, the intermediateresistance walls extending from the diverging side walls of the troughshaped lower part, and slant upwardly toward the center plane toenclose, with the lower portion corresponding to it, a space which isproportionately smaller than and generally similar in section to that ofthe whole burner, the flame opening in each resistance wall beingnarrower than any flame opening above it, the flame opening in theresistance wall closest to said primary flame opening being considerablysmaller than said primary flame openmg.

5. Apparatus according to claim 4, in which the side walls of the lowerportion are made stairstep-shaped with a number of steps correspondingto the number of intermediate resistance walls that divide the interiorof the burner.

6. Apparatus according to claim 5, in which the lowermost of thehorizontal parts of the stairstep shaped side walls of the lower portionof the burner pot serves at the same time for carrying one of saidroof-shaped intermediate resistance walls.

7. Apparatus according to claim 5, in which the air inlet openings inthe burner pot are arranged at the reentering angles of thestairstep-shaped side walls.

8. Apparatus according to claim 7, in which the air inlet openings aredirected generally to the mouth of the spaces formed by the roof-shapedintermediate resistance walls.

9. The pot burner of claim 1, in which each of said additional air inletopenings in said upstanding walls is so spaced as not to be opposite anair inlet opening in the opposed wall.

10. The pot burner of claim 9, in which means are provided to close saidadditional air inlet openings in said upstanding walls.

11. The pot burner of claim 1, in which at least one pair ofintermediate upwardly converging roof shaped elements is provided belowsaid primary air openings and lying generally parallel to said upperportions, said pair of intermediate elements terminating short of thecenter plane of the burner to provide a secondary flame opening narrowerthan said primary flame opening, the space enclosed by the lower portionof said trough shaped lower portion and said pair of intermediateelements being substantially the same shape as, but proportionatelysmaller than, the space enclosed by the entire trough shaped lowerportion and said roof shaped upper portions, and second air openingssolely in the diverging walls ofrsaid lower portion having means todirect inflowing air upwardly and inwardly from each side of said lowerportion in a plane, the planes of said inflowing air intersectingclosely below said second flame opening.

12. The pot burner of claim 11, in which at least two pairs ofintermediate upwardly converging elements are provided, each said pairof intermediate elements providing a flame opening proportionatelysmaller than the flame opening of the pair of roof shaped elementspositioned above it, and being provided with air inlet openings havingmeans to direct air from each side of said trough shaped lower portionin planes intersecting just below the corresponding flame opening.

13. A pot burner comprising a bottom portion having upwardly divergingwalls on each side of at least one plane of symmetry, an upper portionhaving converging walls extending upwardly and inwardly from the upperedge of said upwardly diverging walls, said converging walls terminatingshort of said plane of symmetry to provide a primary flame opening, saidupper and lower portions bounding an enclosure of generallydiamondshaped cross section, at least one intermediate resistance wallextending from the diverging walls of said lower portion below the upperedge thereof and converging upwardly and inwardly generally parallel tosaid upper portion to provide a secondary flame opening at the top edgesof said resistance wall to enclose, with the part of said lower portioncorresponding to said resistance wall, a space that is generallydiamond-shaped in cross section proportionately smaller than, andgenerally similar in section to that of the entire burner, the secondaryflame opening in said intermediate resistance wall being smaller thanthe primary flame opening of the entire burner, and air openings solelyin said diverging walls of said lower portion both above and below saidresistance. wall including means to direct inflowing air upwardly andinwardly into the generally diamondshaped enclosures so that the streamsof air inflowing through said openings intersect each other closelybelow the corresponding primary or secondary flame opening.

References Cited in the file of this patent UNITED STATES PATENTS2,212,078 Sabins Aug. 20, 1940 2,214,670 Gilmore et a1. Sept. 10, 19402,241,470 Miller May 13, 1941 2,244,766 Cooper June 10, 1941 2,311,469Pruitt Feb. 16, 1943 2,337,673 McCurtain Dec. 28, 1943 2,422,209 Reeveset al. June 17, 1947 2,428,009 Breese Sept. 30, 1947 2,494,104 Piatt etal. Jan. 10, 1950 2,519,570 Hayter Aug. 22, 1950 2,538,911 Reeves Ian.23, 1951 2,581,238 Cauley Ian. 1, 1952 2,638,160 Thomson May 12, 19533,017,921 Stierlin Jan. 23, 1962 FOREIGN PATENTS 148,864 Australia Nov.3, 1952 1,101,121 France Apr. 13, 1955 OTHER REFERENCES Handbook of OilBurning, pub. by Oil-Heat Institute of America Inc, copyright 1951,pages 174 and 175.

1. A POT BURNER COMPRISING AN ELONGATED TROUGH SHAPED LOWER PORTIONFORMED WITH UPWARDLY DIVERGING WALLS SYMMETRICALLY ON EACH SIDE OF ACENTER PLANE, ROOF SHAPED UPPER PORTIONS EXTENDING UPWARDLY FROM THEUPPER EDGE OF EACH WALL OF SAID LOWER PORTION AND CONVERGING UPWARDLY TOBOUND, WITH SAID LOWER PORTION, A GENERALLY DIAMOND SHAPED ENCLOSURE,SAID UPPER PORTIONS TERMINATING SHORT OF THE CENTRAL PLANE OF SAID LOWERPORTION TO FORM A FLAME OPENING, PRIMARY AIR OPENINGS SOLELY IN THEDIVERGING WALLS OF SAID LOWER PORTION, SAID AIR OPENINGS HAVING MEANS TODIRECT INFLOWING AIR UPWARDLY AND INWARDLY FROM EACH SIDE OF SAID LOWERPORTION IN A PLANE, THE PLANES OF SAID INFLOWING AIR INTERSECTING BELOWSAID PRIMARY FLAME OPENING, SAID CONVERGING UPPER PORTIONS TERMINATINGAT SAID PRIMARY FLAME OPENING IN OPPOSED GENERALLY PARALLEL UPSTANDINGWALLS, SAID UPSTANDING WALLS BEING PROVIDED WITH ADDITIONAL AIR INLETOPENINGS TO DIRECT AIR ACROSS SAID PRIMARY FLAME OPENING IN PLANESNORMAL TO SAID CENTER PLANE.